A matrix is a rectangular array of numbers or variables. It consists of rows and columns. For example, consider the following matrix:

[ 1  2  3 ]
[ 4  5  6 ]

In this matrix, there are 2 rows and 3 columns. The numbers in the matrix are called elements. You can perform operations on matrices, such as addition and multiplication, following specific rules. Matrices are used to solve systems of linear equations, transform geometric shapes, and represent data in various applications.